Various techniques have been employed for transferring or transporting thermal energy between a thermal source and a thermal sink or load. One technique or means often used employs a heat pipe. The heat pipe is connected between the heat source and the heat sink and a transport medium therewithin is caused to flow between the two positions to transfer thermal energy from the source to the sink. A basic form of heat pipe employs a vaporization/condensation cycle or mode of operation for effecting the requisite thermal energy transfer. In that type of heat pipe, there is rapid heat transfer into the pipe resulting in vaporization of a liquid transport medium therein. The evaporated transport medium builds up sufficient pressure to be transported along the pipe and is then condensed at the heat sink position. The cycle is completed by returning the condensate to the evaporating end by means of capillary or other action through a wick or other suitable means within the pipe. Typically, the working fluid may be water, freon, methyl alcohol, acetone or the like. The heat of vaporization is such that significant quantities of heat may be absorbed during the vaporization of the transport liquid and subsequently released at the heat sink during its condensation.
Because the thermal energy transported in a vaporization/condensation type of heat pipe is transported at the elevated temperatures of the vaporized transport medium, the opportunity for heat loss during transport by radiation, convection and/or conduction may be significant, particularly if the transport distance is greater than tens of feet. In instances in which thermal energy is to be transported relatively long or significant distances, for instance from tens or hundreds of feet to as much as tens or hundreds of miles, and it is desired to minimize thermal losses during transport, chemical heat pipes can be employed. In such heat pipes, a reactant or reactants undergo a first chemical reaction at the heat source and a second chemical reaction at the heat sink. The reactions are generally reversible, with the first being of an endothermic nature in which heat is chemically absorbed by the reaction process and with the second being exothermic in which heat is chemically liberated during the reaction process. The reactant and/or reaction products may exist and be transported at temperatures which do not differ substantially from that of the environment, thereby greatly reducing the potential for thermal loss from the system. In such chemical heat pipes, most of the thermal energy absorbed from the source occurs by virtue of the endothermic reaction, with relatively little heat being absorbed by evaporation. An example of one such chemical heat pipe is disclosed in copending U.S. application Ser. No. 226,320 entitled Self-driven Chemical Heat Pipe by A. S. Kesten and A. F. Haught, filed on even date herewith and assigned to the assignee of the present application.
Although heat pipes of the chemical reaction type may be particularly suited for the long-distance transport of thermal energy, the sometimes simpler and less expensive vaporization/condensation type of heat pipe is used almost exclusively for situations in which the distance over which the thermal energy to be transported is relatively short, for instance less than tens of feet and for those situations in which the source temperature and/or the source-sink temperature difference is insufficient for a suitable chemical heat pipe reaction. The vaporization/condensation type heat pipe is generally self-driven and the rate of thermal energy transport is determined by the transport medium, by the relevant operating temperatures and by the geometry of the system. Generally, the rate of heat transport in a system in which the evaporation and condensation surface areas are relatively small will be less than that for which those surfaces are relatively large, other factors being equal. Various physical constraints and/or cost considerations may however, interfere with or prevent the provision of a vaporization/condensation heat pipe of sufficient physical capacity for the task intended.
Accordingly, it is a principal object of the present invention to provide a heat pipe of the vaporization/condensation type with enhanced operating capabilities. Included in this object is the provision of a method for enhancing the rate of thermal transport in vaporization/condensation heat pipes of particular and limited geometries.